Shells and languages I've not used for a substantial part of a real project don't qualify.

I'm at my best in UNIX-like environments, though I've done Win32 programming in C, and if you'd guessed the C# I wrote ran on Windows, you'd be right.

I believe efficient code is still a virtue. I don't believe in optimizing at the expense of maintainability without just cause, but far too often I see code written that is senselessly inefficient and harder to maintain (or bug-ridden).

Now, to hijack some quotes:

More computing sins are committed in the name of code reuse (without necessarily achieving it) than for any other single reason - including blind stupidity.